Acetabular reamer

ABSTRACT

An acetabular reamer includes a base, a first set of semi-circular blades attached to the base, and a second set of semi-circular blades also contacting said base, and crossing and intersecting with said first set of blades at right angles thereto. The base preferably comprises a circular plate having a hexagonal drive hole in the center thereof and a plurality of slots in the periphery thereof for anchoring the blades. Each semi-circular blade includes a first end having a projection thereon, a second end opposite from said first end and also having a projection thereon, a first edge having serrated cutting teeth thereon, a second edge opposite from said first edge, and a first and second side surface. The cutting edge of the first set of blades includes a plurality of outwardly facing slots which mate with and engage a second set of inwardly facing slots in the second edge of said second blades. When the first and second set of blades are assembled in this fashion the cutting edges of both sets of blades lie in the same spherical plane. The projections can comprise snap-in projections that automatically lock in position or projections that can be twisted and locked into position. Alternatively, the base can comprise a pair of upper and lower plates with apertures in the upper plate such that when the blade projections mate with the apertures, riveting of the lower plate with respect to the upper plate locks the projections and their related blades into position on the base. When the reamer is assembled it has a hemispherical shape suitable for reaming the acetabulum of the hip so that the acetabular portion of a hip implant properly fits into the acetabulum.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a multi-blade acetabular reamer and a methodfor constructing the same.

2. Description of Related Art

The prior art patent literature describes a few reamers and cutters forremoving bone and tissue from joints that may be relevant to the stateof the art. For example, U.S. Pat. No. 4,621,637 entitled "SURGICALDEVICE FOR REMOVING BONE AND TISSUE FROM JOINT MEMBERS" teaches aslotted, surgical device including a hemispheric housing that supportsone or more cutting blades for bone and/or tissue cutting. Two and threeblade embodiments are described. In both cases, the blades abutcentrally of the device and interlock with the base at discrete points.

French Patent 1,031,888 describes a plurality of cutting blades whichare radially disposed, equiangularly spaced atop a supporting plate andlocked to the plate by fasteners. The resulting tool is used for cuttingthe acetabular portion of a hip prior to joint replacement.

Similarly, French Patent 1,041,311 describes a bone cavity forming toolwhich employs multiple blades in a hemispheric array.

Soviet Union Patent 1225-543-A entitled "BONE CUTTING TOOL FOR SURGERY"describes a cutter comprising multiple arcuate cutting elementsextending from a central rod outwardly in an umbrella fashion.

French Patent 2,233,972 entitled "ARTIFICIAL HIP JOINT FITTINGEQUIPMENT" describes another multi-blade, round headed milling cutterfor acetabular application.

U.S. Pat. No. 5,222,959 entitled "REMOVAL OF TISSUE" describes a softtissue cutter having an oval, rather than hemispheric, shape.

U.S. Pat. No. 5,192,291 entitled "ROTATIONALLY EXPANDABLE ATHERECTOMYCUTTER ASSEMBLY" describes another soft tissue cutter in which theblades define a cylindrical, not hemispheric, structure.

U.S. Pat. No. 5,100,267 entitled "DISPOSABLE ACETABULAR REAMER CUP"describes a hemispheric, cup-shaped hip reamer. With regard to thisstructure, note also U.S. Pat. Nos. 5,116,165 and 5,376,092.

The following U.S. Patents describe prior art bone reamers of possibleinterest, using multi-blade configurations, but for non-hipapplications: 3,554,192; 5,122,134, 5,180,384 and 5,318,576.

Lastly, U.S. Pat. No. 3,633,583 entitled "ORTHOPEDIC SINGLE-BLADE BONECUTTER" is of general relevance only.

While a few joint reamers arc known in the prior art, they tend to beexpensive, or hard to construct, or both. There clearly appears to be aneed for a safe, easy to assemble, inexpensive and effective reamerespecially for the acetabulum of the hip. Insofar as understood, none ofthe prior art known to the inventor, whether taken individually or incombination, hints, teaches or suggests the novel acetabular reamerdisclosed herein.

SUMMARY OF THE INVENTION

Briefly described, the invention comprises an acetabular reamerincluding a base, a first set of three semi-circular blades attached tothe base, and a second set of three semi-circular blades also attachedto the base, but at right angles to said first set of blades. The firstset of three blades includes a major blade that spans the entirediameter of the circular base, and a pair of smaller, minor blades, thatspan a shorter chord of the circular base. Likewise, the second set ofblades includes a major blade that spans the greater diameter of thecircular base and a pair of smaller, minor blades that span a lesserchord. Each of the semi-circular blades includes a first and a secondend, an exterior cutting edge, an interior edge opposite from saidcutting edge, and a pair of side faces. The first and second end of eachof the blades includes a projection which is receivable in a slottedaperture on the periphery of the circular base. Each of the three bladesof the first set of blades includes three slots on the outer cuttingedge thereof which engage respectively with one of three slots locatedon the interior edge of each of the three blades of the second set. Theapparatus is first assembled by engaging the slots of the first set ofthree blades with the slots of the second set of three blades so thatthe ultimate structure has a three dimensional shape and the cuttingsurfaces of said first and second set of blades are at the same levelwhere said blades intersect.

According to the preferred embodiment of the invention, the projectionson the blades include a pair of prongs that snap and lock into theperipheral apertures on the base. According to an alternative embodimentof the invention the projections, or tabs, extend through the aperturesin the base and can be locked in place by twisting them with respect totheir respective slots so they cannot back out. According to anotherembodiment of the invention, the base comprises a pair of upper andlower plates wherein the lower plate locks the projections into theperipheral slots of the upper plate.

These and other features of the invention will be more fully understoodby reference to the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the preferred embodiment of theacetabular reamer invention.

FIG. 2 is an exploded view of the preferred embodiment illustrated inFIG. 1.

FIG. 3 is a bottom plan view of the base of the preferred embodimentillustrated in FIG. 1.

FIG. 4 illustrates the largest of the cutter blades having inwardlyfacing slots according to the preferred embodiment of the invention.

FIG. 5 illustrates the largest of the cutter blades having outwardlyfacing slots according to the preferred embodiment of the invention.

FIG. 6 illustrates a blade according to a first alternative embodimentof the invention in which the cutting blades are anchored and lockedinto position in the peripheral slots in the base by a pair ofprojections each including a pair of spring loaded elements.

FIG. 7 is a perspective view of a second alternative embodiment of theinvention which employs two base plates to lock the cutting blades inposition.

FIG. 8 is an exploded view of the second alternative embodiment of theinvention illustrated in FIG. 7.

FIG. 9 is a bottom plan view showing the base of the second alternativeembodiment of the invention as illustrated in FIGS. 7 and 8.

FIG. 10A illustrates a cutter blade having inwardly facing slotsaccording to the second alternative embodiment of the inventionillustrated in FIGS. 7-9.

FIG. 10B illustrates another cutter blade having complimentary,outwardly facing slots, that mates with the blade of FIG. 10 and issuitable for use with the second alternative embodiment of the inventionillustrated in FIGS. 7-9.

FIG. 11A illustrates a cutter blade having inwardly facing slots andincluding a cutting surface having oval cutouts.

FIG. 11B illustrates a cutter blade having complimentary, outwardlyfacing slots, that mate with a blade of FIG. 11 also including ovalcutouts that form its cutting surface.

FIG. 11C illustrates a cutter blade having inwardly facing slots andhaving a cutting edge that comprises a plurality of teeth that areseparated by semi-circular cutouts.

FIG. 11D illustrates a cutter blade having complimentary, outwardlyfacing slots, that mate with the blade of FIG. 11C also including acutting edge that comprises a plurality of flat teeth separated bysemi-circular cutout portions.

FIG. 11E illustrates a cutter blade having inwardly facing slots andhaving a cutting edge that includes a plurality of arcuate cuttingslots.

FIG. 11F illustrates a cutter blade having complimentary, outwardlyfacing slots that mate with the blade of FIG. 11E and also includes acutting edge incorporating a plurality of arcuate cutting slots.

FIG. 12A is a bottom plan view of the upper, or top base plate accordingto the embodiment illustrated in FIGS. 7-10B.

FIG. 12B is a bottom plan view of the bottom, or lower base plate of theembodiment illustrated in FIGS. 7-10B.

FIG. 12C illustrates another, upper base plate suitable for use with theembodiment of FIG. 7-10B but including a larger, central, hexagonaldrive hole.

FIG. 12D illustrates another, lower, base plate suitable for use withthe embodiment illustrated in FIG. 7-10B but including a larger,central, hexagonal drive hole that matches the drive hole of the upperplate illustrated in FIG. 12C.

FIG. 12E illustrates another, upper base plate suitable for use with theembodiment of FIG. 7-10B but including an X-shaped center.

FIG. 12F illustrates a bottom, or lower plate suitable for use with theembodiment of FIG. 7-12B, and including an X-shaped central drivesection complimentary to the X-shaped drive section of the upper baseillustrated in FIG. 12E.

DETAILED DESCRIPTION OF THE INVENTION

During the course of this description like numbers will be used toidentify like elements according to the different figures thatillustrate the invention.

The preferred embodiment 10 of the invention is illustrated in itsassembled form in FIG. 1 and in an exploded form in FIG. 2. The basicelements of the preferred embodiment 10 are a base 12, a first set 18 ofcutter blades (20, 22, 24) and a second set 26 of mating cutter blades(28, 30, 32). The base 12, as seen in FIGS. 2 and 3, includes twelveperipheral slots 14 and a hexagonal center hole 16 suitable for mountingthe acetabular reamer 10 on a drill. Slots 14 are arranged in fourgroups of three set at 90° with respect to each other.

The first group 18 of blades includes a larger cutter blade 20 thatsubstantially spans the longest dimension, i.e., the diameter, of base12. A pair of smaller, minor cutter blades 22 and 24 are located onopposite sides of the larger blade 20, and dissect a smaller chord ofthe circular base 12.

FIG. 4 illustrates the larger cutter blade 20 in greater detail. Smallerblades 22 and 24 are not illustrated because they both have asubstantially identical shape. Larger cutter blade 20 includes a first,outwardly facing edge 40 including a plurality of serrated teeth 42. Thesize and dimension of teeth 42 may vary depending upon the nature of thehip socket that needs to be reamed. Large blade 20 also includes a firstend 44 having a projection, or tab, 46 thereon and a second end 48opposite, or distal from the first end 44 also including a tab orprojection 50 thereon. Tabs 46 and 50 engage with, and pass through, apair of slots 14 on opposite sides of base 12. Blade 20 also has asecond edge 52, opposite the first edge 40, that includes three inwardlyfacing slots 54a, 54b and 54c. The remaining two blades 22 and 24 of thefirst group 18 also include three inwardly facing slots similar to slots54a, 54b and 54c of blade 20. Lastly, blade 20 includes a first broadside face 56 and a second broad side face 58 on the opposite surfacefrom face 56. Similarly, smaller blades 22 and 24 also include opposingbroad side faces.

The largest cutter blade 28, from the second group of blades 26 isillustrated in FIG. 5. Like blade 20, blade 28 includes a first edge 60including a plurality of sharp cutter teeth 62 opposite from an inwardlyfacing edge 72. Blade 28 further includes a first end 64 having alocking tab 66 and a second end 68, opposite, or distal from, the firstend 64 also including a locking tab 70. A first broad, side face 76 islocated opposite from a second broad side face 78. Large blade 28further includes three outwardly facing slots 74a, 74b and 74c. Blades30 and 32, of second group 26, also include three slots, respectively,similar in shape and location to slots 74a, 74b and 74c of blade 28.

When the acetabular reamer 10 is assembled the three blades 20, 22 and24 from the first group 18 are placed over the blades 28, 30 and 32 ofthe second group 26 so that one slot 54a, 54b or 54c from a blade in thefirst group 18 matches and mates with a second slot 74a, 74b or 74c froma blade in the second group 26. For example, inwardly facing slot 54b ofblade 26 mates with and engages with outwardly facing slot 74b of blade28. Once the blades 20, 22, 24, 28, 30 and 32 have been mated andmatched, they form an egg crate-like cross section in which the teeth 42and 62 on the exterior edges 40 and 60 all lie in the same sphericalplane. When assembled in this fashion, the locking tabs 46, 50, 66 and70 line up with, and pass through, the peripheral slots 14 in the base12. Once the tabs 46, 50, 66 and 70 pass through their respective slots14 they can be twisted, and locked, in position as illustrate in FIG. 3.The reamer 10 can then be placed on an appropriate drill bit and rotatedat the desired speed to ream a socket in the hip bone of a patient.

The method of assembly just described is relatively fast and economical.The reamer blades 20, 22, 24, 28, 30 and 32 can be cut with conventionallaser equipment from medical grade steel. Fabrication and assembly canbe performed in a matter of a few minutes.

FIG. 6 illustrates a first alternative embodiment 80 of a snap-in cutterblade. Snap-in cutter blade 80 includes a pair of resilient projections,or tabs, 82, located on the first and second end thereof. Each tab 82includes a pair of opposite facing, L shaped elements 84 and 86. Theremaining five blades of the group have tabs similar to 82. Once the sixcutter blades have been assembled in the manner previously describedwith reference to the preferred embodiment 10, the tabs 82 are placedinto peripheral slots 14. When the tabs 82 are forced into slots 14 theyeventually snap into place thereby locking the six blades securely inposition on the base 12.

A second alternative embodiment of the invention 90 is illustrated inassemble form in FIG. 7 and in an exploded view in FIG. 8. FIG. 9illustrates the base 92 of the alternative embodiment 90 as seen frombelow. FIG. 10A illustrates the larger cutter blade 100 from the firstgroup 120, whereas FIG. 10B illustrates the larger blade 104 from thesecond group 118.

The base 92 of the second preferred embodiment 90 includes a first upperbase plate 94 and a second, lower, locking base plate 96. The first baseplate 94 has a structure virtually identical to base plate 12 of thepreferred embodiment 10 except that it includes a pair of rivetaccepting holes 122. First base plate 94 also includes four sets ofthree slots 14 each positioned at 90° with respect to each other and ahexagonal central drive hole, or aperture, 16. The second, or lowerlocking plate 96, also includes a hexagonal shaped central drive hole126 which lines up with drive hole 16 of the first plate 94. Lockingplate 96 has a generally S-shaped configuration and has a pair of rivetaccepting holes 124 which line up with holes 122 in the first, or upper,plate 94 when plates 94 and 96 are in proper alignment for locking theblades from the first and second sets 120 and 118. A pair of rivets 98secures plates 94 and 96 together when holes 122 and 124 are properlyaligned and then rivets 98 are swaged to lock plates 94 and 96 in rigidposition.

The first set 120 of three blades 100, 110 and 112 can be more fullyunderstood by referring to FIGS. 8 and 10a. The larger blade 100 isillustrated in FIG. 10A and is shown to include a pair of inwardlyfacing, L-shaped tabs 102 at the first and second ends thereof.Likewise, the smaller adjacent cutting blades 110 and 112 also includeinwardly facing L-shaped tabs 102 similar to blade 100. Otherwise, theshape of the blades 100, 110 and 112 is similar to that of blades 20, 22and 24 of group 18 of the preferred embodiment 10 illustrated in FIG. 1,in that they each include three inwardly facing slots.

In contrast, the three blades 104, 114 and 116 of the second group 118have a different tab 106 configuration as seen in FIGS. 8 and 10b. Thelarger cutter blade 104 of the group 118 is illustrated in FIG. 10B andis shown to include a pair of straight tabs 106 at the first and secondend thereof. Tabs 106 do not have inwardly or outwardly facingprojections and are shorter in length than the inwardly facing, L-shapedtabs 102 shown on blade 100 of FIG. 10A. Blades 114 and 116 also includeshort, stubby tabs 106 at the first and second ends thereof. Tabs 106are intended to fit into peripheral slots 14 in the plate 94 but do notnecessarily protrude all the way through. The purpose of tabs 106 is tohold blades 104, 114 and 116 of the second group 118 in position onplate 94. In contrast, the purpose of the L-shaped locking tabs 102 onblades 100, 110 and 112 of the first group 120 is to be engaged by thelower plate 96 and locked into position with respect to the base 92.Because the blades 100, 110 and 112 of the first group 120 are locatedabove the blades 104, 114 and 116 of the second group 118, the blades ofgroup 18 are automatically held in position even if they are not locked,i.e., anchored, directly with respect to base plate 94. As shown inFIGS. 10A and 10B, blades 100 and 104 (as well as 110, 112, 114 and 116)all include triangular cutting teeth 108. Lower blade 104 has a maximumoutside diameter A in the range of 36 millimeters to 82 millimeters(1.417 to 3.228 inches). The upper major cutting blade 100 has a maximumexterior diameter B in the same range.

The second alternative embodiment 90 illustrated in FIGS. 8-10b isassembled in the following manner.

First, the nine outwardly facing slots in blades 104, 114 and 116 ofsecond group 118 are aligned, at right angles, with the respectivelyinwardly facing slots of blades 100, 110 and 112 of first group 120, ina manner identical to that described with regard to the first step ofthe assembly of the preferred embodiment 10.

Second, the six loosely assembled blades are placed over first, upperbase plate 94 so that all tabs 102 and 106 pass into their respectivetwelve receiving slots 14. As previously described, the stubby, shortertabs 106 on blades 104, 114 and 116 of second group 18 do notnecessarily pass all the way through their six respective receivingslots 14 in the first plate 94. Rather, the purpose of tabs 106 inperipheral slots 14 is to hold the blades into position rather than tolock them there. In contrast, the inwardly facing L-shaped tabs 106 onblades 100, 110 and 112 of second group 120 clearly pass through thebottom of the first, upper plate 94 enough so that all six of them canbe engaged by the second, or lower locking plate, 96. There is enough ofa gap in this configuration that locking plate 96 can be slid into thespace between L-shaped tabs 102 and the upper, or first plate, 94 sothat the tabs 102 cannot back out of slots 14. When properly inposition, the rivet apertures 124 of the second lower plate 96 line upwith, and are coaxial with, the rivet apertures 122 in the first plate94.

Third, and last, a pair of rivets 98 is placed through coaxial holes 122and 124 and swaged into position there so that plate 96 will permanentlyhold inwardly facing L-shaped tabs 102 in position in their respectivesix locking slots 14 in the first plate 94.

The second alternative embodiment 90 is significantly less expensive tomanufacture and produce than prior art reamers. It is also very easy toassemble and can be put together in a satisfactory, permanent manner ina matter of minutes.

FIGS. 11A and 11B describe a pair of upper and lower blades 120 and 124having a cutting edge that includes a plurality of oval cutout sections128. Tabs 122 and 126 are employed for attachment to a base 92 aspreviously described. FIGS. 11C and 11D illustrate another pair ofcutting blades 140 and 144 which include a cutting edge having aplurality of flat teeth 148 separated by semi-circular cutouts. Aspreviously described, with regard to the embodiment of FIG. 11A and 11B,tabs 142 and 146 mate with base 92 such as illustrated in FIG. 8.Lastly, FIGS. 11E and 11F illustrate another pair of cutting blades 160and 164 which include a plurality of arcuate cutting slots 168 on theircutting edge. Again, tabs 162 and 166 are intended to engage a base 92such as illustrated in FIG. 8. While triangular teeth 108 such asillustrated in FIGS. 10A and 10B is the preferred cutting edge orsurface, it is clear that a variety of other cutting topographies suchas ovals 128, semi-circular cutout teeth 148 or arcuate slots 168 couldbe employed as well depending upon the nature of the cutting job to beperformed.

In addition, modifications can be made to the base 92 as illustrated inthe embodiment shown in FIG. 8. FIGS. 12A and 12B, respectively,illustrate the upper base plate 94 and the lower base plate 96 of thebase 92 of embodiment 90. Upper plate 96 includes a hexagonal drive hole16 having a dimension C of approximately 0.75 inches. Likewise, thelower base plate 96 includes a hexagonal drive aperture 126 having adimension C also equal to 0.75 inches. Clearly, hexagonal drive hole 16and 126 have identical shapes and dimensions. FIGS. 12C and 12Dillustrate, respectively, an alternative upper base plate 194 and lowerbase plate 196. Upper base plate 194 includes a hexagonal central drivehole 16 having a dimension D of 1.018 inches. Likewise, the hexagonalcentral drive hole 126 of the lower base plate 196 also has a dimensionD equal to 1.018 inches. The size of hexagonal drive hole 16 and 126 mayvary depending upon the nature of the driving device and the materialbeing reamed. Lastly, FIG. 12E and 12F, respectively, show an upper baseplate 194 and a lower base plate 196. Upper base plate 294 includes anX-shaped central drive section 300 and four pie shaped cut out apertures302 surrounding the X-shaped central section 300. Likewise, the lowerbase plate 296 includes an X-shaped central drive section 298 and fourpie-shaped cutout apertures 290 surrounding the X-shaped central drivesection 298. The cross arms of the X-shaped central drive sections 298and 300 have a dimension E of approximately 0.195 inches. X-shapedcross-section 298 is substantially identical in shape and dimensions toX-shaped central drive section 300. The embodiments in FIGS. 12A-12Fillustrate the fact that the variety of different, central drivesections may be employed depending upon the nature of the driving unitand the demand placed upon the reamer.

While the invention has been described with reference to the preferredembodiment thereof, it will be appreciated by those of ordinary skill inthe art that modifications and changes can be made to the structure andfunction of the invention without departing from the spirit and scopethereof.

We claim:
 1. An acetabular reamer apparatus comprising:a base includinga plurality of apertures therein; a plurality of first blade means eachincluding a first end with a projection thereon receivable in anaperture in said base, a second end distal from said first end and alsoincluding a projection thereon receivable in an aperture in said base, afirst edge having a cutting surface thereon and including a slot meanstherein, and a second edge opposite from said first edge; a plurality ofsecond blade means each having a first end for contacting said base anda second end opposite from said first end and also for contacting saidbase, a first edge having a cutting surface thereon and a second edgeopposite from said first edge including slot means therein, wherein saidslot means in said first blade means mate and engage with slot means insaid second blade means and wherein said first and second blade meanscross each other to form a three dimensional acetabular cutting surfacewhen said apparatus is rotated.
 2. The apparatus of claim 1 wherein saidcutting surfaces on said blade means include cutting teeth.
 3. Theapparatus of claim 2 wherein said first blade means comprises at leasttwo blades and said second blade means comprises at least two bladesthat cross said two blades of said first blade means substantially atright angles.
 4. The apparatus of claim 3 wherein said first blade meanscomprises three blades and said second blade means comprises threeblades that cross said three blades of said first blade means at rightangles.
 5. The apparatus of claim 4 wherein said base is substantiallycircular and includes a drive aperture in the center thereof.
 6. Theapparatus of claim 1 wherein said projections on said first and secondblade means snap into said apertures in said base and automatically lockwith respect thereto.
 7. The apparatus of claim 1 wherein saidprojections on said first and second blade means can be inserted intosaid apertures in said base and twisted to lock said first and secondblade means with respect to said base.
 8. The apparatus of claim 1wherein said base comprises:a first plate having projection receivingapertures therein; and, a second plate, wherein attaching said secondplate with respect to said first plate causes said projections to lockin position said first blade means with respect to said first plate. 9.The apparatus of claim 1 wherein said cutting surfaces on said blademeans include a plurality of oval cutout sections.
 10. The apparatus ofclaim 1 wherein said cutting surfaces on said blade means include aplurality of teeth separated by semi-circular cutout sections.
 11. Theapparatus of claim 1 wherein said cutting surfaces on said blade meansincludes a plurality of arcuate, cutting slots.
 12. The apparatus ofclaim 1 wherein said base is substantially circular and includes ahexagonal drive aperture in the center thereof.
 13. The apparatus ofclaim 1 wherein said base is substantially circular and includes anX-shaped, drive engaging section in the center thereof.
 14. Anacetabular reamer apparatus comprising:a base; a plurality of firstblade means each having a first end attached to said base, a second enddistal from said first end and also attached to said base, a first edgehaving a cutting surface thereon, and a second edge opposite from saidfirst edge; a plurality of second blade means each having a first endfor contacting said base and a second end distal from said first end andalso for contacting said base, a first edge having a cutting surfacethereon and a second edge opposite from said first edge, wherein saidplurality of first and second blade means cross each other to form athree dimensional acetabular cutting surface when said apparatus isrotated.
 15. An acetabular reamer apparatus comprising:a base; aplurality of first blade means each having a first end attached to saidbase, a second end distal from said first end and also attached to saidbase, a first edge having a cutting surface thereon, and a second edgeopposite from said first edge; a plurality of second blade means eachhaving a first end for contacting said base and a second end distal fromsaid first end and also for contacting said base, a first edge having acutting surface thereon and a second edge opposite from said first edge,wherein said plurality of first and second blade means cross each otherat substantially right angles to form a three dimensional acetabularcutting surface when said apparatus is rotated.